Product acceptance/rejection judgement method for an injection molding machine

ABSTRACT

A product acceptance/rejection judgment method which always ensures accurate judgment whether a product is acceptable or not even when an injection molding machine is operated in different operating environments is implemented by a processor (22) of a numerically controlled device (20). When the processor determines that it should perform, in addition to a normal product acceptance/rejection judgment based on molding process parameters, an auxiliary product acceptance/rejection judgment based on at least one operating parameter which directly indicates an injection molding machine operating environment characteristic involved in the acceptance/rejection judgment of the product, the processor reads output data from an A-D converter (11, 12 or 13) which data corresponds to the actual value of at least one operating parameter detected by an appropriate die temperature sensor (8), open air temperature sensor (9) or a wind velocity sensor (10). If an actual value of any one of the operating parameters deviates from the tolerance limit, and the processor determines that a molding failure may have occurred, the processor issues a failure signal. If all actual values of at least one operating parameter are within the tolerance limits, then the normal product acceptance/rejection judgment process is further implemented.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a product acceptance/rejection judgmentmethod for an injection molding machine, and more particularly, to aproduct acceptance/rejection judgment method which makes it possible toaccurately determine whether a product is acceptable or not at all timeseven when an injection molding machine is operated in various operatingenvironments.

2. Description of the Related Art

It is known that a product sample taken out from a group of productsthat have been mass-produced by repeating a molding cycle is visuallycompared with a non-defective sample to determine whether it isacceptable or not. However, such visual inspection cannot ensureaccurate judgment criteria, and also the non-defective sample changes onstanding. For this reason, the product acceptance/rejection judgmentbased on visual inspection presents such problems as low reliability.Conventionally, therefore, it is judged whether or not the actual valuesof molding process parameters (cushion amount, injection time, meteringtime, metering completion point, injection pressure peak value, screwposition where the injection speed control mode is switched to theinjection pressure control mode, etc.) which are all related to theacceptance/rejection of a product are within tolerance limits during amolding cycle, and the product is determined to be defective if any ofits molding process parameters is found to deviate from the tolerancelimits.

However, when the injection molding machine is operated in differentoperating environments, there are some cases where defective unitsresult even when molding cycles are implemented under molding conditionsthat should produce non-defective units, with all molding processparameters being within tolerance limits. This means that accurateproduct acceptance/rejection judgment may not be performed according tothe aforementioned conventional method wherein the productacceptance/rejection judgment is made based on molding processparameters.

The major reason for this is considered that the conventional methoddoes not adequately take into account operating environment changesinvolved in determining whether a product is acceptable or not. If theoperating environments of an injection molding machine change,corresponding molding process parameter values change accordingly,therefore, the operating environment changes are indirectly consideredin the conventional acceptance/rejection judgment. For instance, if awindow of a factory which is usually closed is opened to let wind blowonto a die installed on an injection molding machine, causing the die tobe cooled, then the injection time increases. And if the injection timeexceeds its tolerance limit, then the product molded at that time isdetermined to be defective. However, it takes time for a molding processparameter value to deviate from its tolerance limit after a defectiveunit results from an operating environment change. During that time,therefore, accurate product acceptance/rejection judgment cannot beimplemented, causing the occurrence of defective units.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a productacceptance/rejection judgment method which makes it possible to alwaysmake accurate judgment whether a unit is defective or not even when aninjection molding machine is operated in different operatingenvironments.

To fulfill the foregoing object, according to the present invention, thevalues of operating parameters which directly indicate the injectionmolding machine operating environments involved in judging the qualityof a product are detected, and if the detected operating parametervalues deviate from tolerance limits, then it is judged that a moldingfailure has taken place.

As described above, according to the present invention, it is judgedthat a molding failure has occurred if the detected values of theoperating parameters which directly indicate the injection moldingmachine operating environments involved in judging the quality ofproducts deviate from tolerance limits, therefore, if any operatingenvironment change that can lead to a molding failure takes place, thenit is immediately determined that a molding failure has occurred.Consequently, even when an injection molding machine is operated indiverse operating environments, accurate product acceptance/rejectionjudgment can be always performed, helping carry out good quality controlof moldings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing the major section of an injectionmolding machine for implementing the product acceptance/rejectionjudgment method according to an embodiment of the present invention;

FIG. 2 is a flowchart showing a molding cycle carried out by theinjection molding machine of FIG. 1; and

FIG. 3 is a flowchart showing a product acceptance/rejection judgmentprocedure carried out by a numerically controlled device shown in FIG.1.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The injection molding machine for carrying out the productacceptance/rejection judgment method according to the embodiment of thepresent invention is provided with various mechanism such as aninjection mechanism, clamping mechanism, and ejector. Referring to FIG.1, the injection mechanism is equipped with a screw 1 installed in aheating cylinder 4, an injection servomotor 2 for driving the screw inthe axial direction, and a servomotor (not shown) for rotating the screw1, and it is designed to inject a molding material (resin) which hasbeen plasticized and kneaded in the heating cylinder 4 into a moldingcavity 5a formed in a die 5 by moving the screw 1 in the axialdirection. A pulse coder 3 for detecting a motor rotational position (aposition on the screw axis) is installed on the injection servomotor 2,and a pressure sensor 6 which comprises, for example, a load cell, fordetecting a resin pressure (an axial reaction force of molten resinapplied to the screw) is mounted on the screw 1. Also, a die temperaturesensor 8 for detecting the die surface temperature is mounted on theexternal surface of the die 5. Further, the injection molding machinehas an open air temperature sensor 9 for detecting the temperature ofthe surrounding air and a wind velocity sensor 10 for detecting thevelocity of the wind around the injection molding machine. A referencenumeral 14 denotes a numidity sensor which is mounted on the injectionmolding machine as necessary to detect the humidity around the injectionmolding machine.

A reference numeral 20 denotes a numerically controlled device (NCdevice) 20 for driving and controlling the diverse mechanisms of theinjection molding machine. The NC device 20 is equipped with amicroprocessor 21 for numerical control (NC CPU) and a microprocessor 22for a programmable machine controller (PMC CPU) to provide a numericalcontrol function and a sequence control function.

More specifically, to the NC CPU 21 are connected a read-only memory(ROM) 24 which stores a control program for controlling an entireinjection molding machine, a random-access memory (RAM) 25 which is usedfor temporarily storing data or the like, and a servo circuit (only theservo circuit related to the injection motor 2 is indicated at 27) fordriving and controlling the servomotors of the individual axes via aservo interface (SSU) 26. The servo circuit 27 is connected to theinjection motor 2 and the pulse coder 3. To the PMC CPU 22 are connecteda ROM 28 wherein a sequence program or the like for controlling thesequential operation of the injection molding machine is stored, a RAM29 which is connected to the pressure sensor 6 via an A-D converter 7and which stores pressure data that is received from the A-D converter 7and that corresponds to a resin pressure detected by the pressure sensor6, and a RAM 30 used for temporarily storing data such as a calculationresult given by the PMC CPU 22.

The NC device 20 is further equipped with a bus arbiter controller (BAC)23 for bus control. To the BAC 23 are connected buses 36 of the CPUs 21and 22, a shared memory 31, an input circuit (DI) 32, and an outputcircuit (DO) 33. The shared memory 31 stores an NC program, moldingconditions, setting values, etc., and comprises a nonvolatile RAM. Toeach of the input circuit 32 and the output circuit 33 are connecteddiverse sensors and actuators (none of the actuators are shown)installed in the diverse mechanisms of the injection molding machine,including the die temperature sensor 8, the open air temperature sensor9, and a wind velocity sensor 10, and servo circuit 27. The sensors 8, 9and 10 are connected to the input circuit 32 via the A-D converters 11,12 and 13 for converting analog sensor outputs to digital signals. Areference numeral 15 indicates an A-D converter matched to the humiditysensor 14, and a reference numeral 35 denotes a manual data input devicewith a CRT display unit (CRT/MDI) connected to the BAC 23 via anoperator panel controller 34.

As discussed in detail later, in the present embodiment, auxiliaryproduct acceptance/rejection judgment based on at least one operatingparameter (die surface temperature, the open air temperature and windvelocity around the injection molding machine, etc.) which directlyindicates the operating environment of the injection molding machinewhich environment is involved in judging the quality of products is madein addition to the conventional product acceptance/rejection judgmentbased on various molding process parameters (cushion amount, injectiontime, metering time, metering completion position, injection pressurepeak value, screw position where the injection speed control mode isswitched to the injection pressure control, etc.). For this purpose, thetolerance limits (upper and lower limit values) of the individualoperating parameters indicating the operating environments that ensuremolding of non-defective units are predetermined by carrying outexperiments or the like before starting mass production of moldings, andthese values and flag information that indicates the type of anoperating parameter to be used for the auxiliary productacceptance/rejection judgment are manually set in the NC device 20.

In relation to the above, the CRT/MDI 35 is equipped with a CRT screen(not illustrated) for displaying parameter setting information used toset the type of operating parameter for making the auxiliary productacceptance/rejection judgment and to set the upper and lower limitvalues of the operating parameters, and a keyboard having operating keysfor manually entering alphanumeric strings for setting the upper andlower limit values of the operating parameters and the flag information.Also, the shared RAM 31 has a memory area for storing the upper andlower limit values of the operating parameters and the flag information.In the following description, symbols TOH and TOL denote the upper endlower limit values of the open air temperature, TDH and TDL the upperand lower limit values of the die surface temperature, and WVH and WVLthe upper and lower limit values of the wind velocity. Further, symbolsFO, FD and FV represent the flags for the open air temperature, diesurface temperature and wind velocity, respectively.

The following describes the operation of the injection molding machinewhich is configured as mentioned above.

First, an operator depresses the key for selecting the parameter settingscreen of the CRT/MDI 35. In response to the key operation, theparameter setting screen (not illustrated) is shown on the CRT screenunder the control of the PMC CPU 22. Then, the operator normally entersby hand successively, through the keyboard of the CRT/MDI 35, at leastone type of operating parameter and the upper and lower limit values ofat least one operating parameter related to one particular type ofproduct, referring to the setting screen. The PMC CPU 22 stores themanually entered upper and lower limit values of the operating parameterin the shared RAM 31, and sets the value of a corresponding flag memoryof the shared RAM 31 to "1." As necessary, the same operation isrepeated according to the same procedure for another type of molding.

When the operation of the injection molding machine is started, the NCdevice 20 controls the injection molding machine as conventionally knownin accordance with the NC program stored in the shared RAM 31, thesequence program stored in the ROM 28, and the molding conditions presetin the shared RAM 31. More specifically, the servo circuit 27 receives adistributing pulse from the NC CPU 21 via the servo interface 26 andalso receives a feedback pulse from the pulse coder 3, determines aspeed command by D/A-converting a deviation of an actual position of theinjection motor 2 from a command position, and determines the actualspeed by F/V-converting an output of the pulse coder. Further, the servocircuit 27 supplies a driving current to the injection motor 2 accordingto a result of the comparison between the speed command and the actualspeed and a torque limit value supplied by the PMC CPU 22 via the outputcircuit 33, thereby controlling the output torque of the injectionmotor. After that, the foregoing injection speed control mode isswitched to the conventional well-known injection pressure control mode.Further, the mechanisms other than the injection mechanism arecontrolled in a well-known mode, and in this way, the conventionalwell-known molding cycle is repeatedly implemented. In each moldingcycle, the PMC CPU 22 sequentially executes a series of processes ofclamping, injecting, holding, making product acceptance/rejectionjudgement, metering, die opening, and ejecting (steps S1 through S7 inFIG. 2).

Referring to FIG. 3, the process of making product acceptance/rejectionjudgment is now explained in detail.

When the process of making product acceptance/rejection judgment isbegun, the PMC CPU 22 first determines whether or not the flag F0 is "1"which indicates that the auxiliary product acceptance/rejection judgmentbased on the open air temperature should be performed (step S401). Ifthe judgment result in the step S401 is negative, then the CPU 22determines whether or not the flag FD is "1" which indicates that theauxiliary product acceptance/rejection judgment based on the die surfacetemperature should be performed (step S405). If the judgment result ofthe step S405 is negative, then the CPU 22 further determines whether ornot the flag FW is "1" which indicates that the auxiliary productacceptance/rejection judgment based on the wind velocity should beperformed (step S409). If this judgment result is negative, andtherefore all the results in the step S401, S405 and S409 are negative,then the CPU 22 executes the normal product acceptance/rejectionjudgment process in a step S413. In the normal productacceptance/rejection judgment process, it is determined whether or notthe detected values of various molding process parameters (cushionamount, injection time, metering time, metering completion point,injection pressure peak value, screw position where the injection speedcontrol mode is switched to the injection pressure control mode, etc.)are within the tolerance limits. If it is found that all molding processparameter values are within the tolerance limits, and therefore judgedthat there is no possibility of any molding failure having taken place,then a chute (not illustrated) which is provided midway on a productcarrying path (not shown) located, for example, at the bottom of theejector, and which separates non-defectives from defectives, is switchedto the non-defectives carrying path side under the control of the NCdevice 20. In this way, the product obtained from that molding cycle iscarried to a non-defectives storing space. On the other hand, if it isfound that any of the moulding process parameter values deviates fromits tolerance limit, and therefore there is a possibility of a moldingfailure having taken place, then the CPU 22 issues a failure signal. Inresponse to the failure signal, the chute is switched to the defectivescarrying path side under the control of the NC device 20 to carry theproduct to a defectives storing space. Then, the CPU 22 begins themetering process (step S5 of FIG. 2) for the subsequent product.

If it is determined that the value of the flag F0 is "1" during the stepS401 in the auxiliary product acceptance/rejection judgment for themolding cycle, then the PMC CPU 22 reads, via the input circuit 32 andthe BAC 23, the output data from the A-D converter 12 which datacorresponds to an analog output of the open air temperature sensor 9 andindicates the actual open air temperature T0 (step 402), and determineswhether the open air temperature T0 exceeds the lower limit value T0L ornot in order to perform the auxiliary product acceptance/rejectionjudgment based on the open air temperature for this molding cycle (stepS403). If the judgment result in the step S403 is positive, then the CPU22 determines whether the open air temperature T0 is below the upperlimit value T0H or not (step S404). If the judgment result of the stepS403 or S404 is negative, which means that the open air temperaturedeviates from the tolerance limits, there is a possibility of a moldingfailure having occurred, therefore, a failure signal is sent out (stepS414), and the process of FIG. 3 for that molding cycle is terminated.When the failure signal is issued, the product obtained from the moldingcycle is carried to the defectives storing space as in the case wherethe failure signal is generated in the normal productacceptance/rejection judgment process.

On the other hand, if both judgment results of the steps S403 and S404are positive, which means that the open air temperature is within thetolerance limits, then the PMC CPU 22 determines whether the value ofthe flag FD is "1" or not (step S405). If the judgment result of thestep S405 is negative, then the program goes to the foregoing step S409.If the judgment result of the step S405 is positive, then the CPU 22reads, via the input circuit 32 and the BAC 23, the output data from theA-D converter 11 which data corresponds to an analog output of the dietemperature sensor 8 and indicates the actual die surface temperature TD(step S406), and determines whether the die surface temperature TDexceeds the lower limit value TDL or not (step S407) in order to performthe auxiliary product acceptance/rejection judgment based on the diesurface temperature. If the judgment result in the step S407 ispositive, then the CPU 22 determines whether the die surface temperatureTD is below the upper limit value TDH or not (step S408). If thejudgment result of the step S407 or S408 is negative, which means thatthe die surface temperature deviates from the tolerance limits, there isa possibility of a molding failure having occurred, and therefore, afailure signal is sent out (step S414), then the process of FIG. 3 forthe molding cycle is terminated.

If both judgment results of the step S407 and S408 are positive, whichmeans that the die surface temperature is within the tolerance limits,then the CPU 22 determines whether the value of the flag FW is "1" ornot (step S409). If the judgment result of the step S409 is negative,then the program goes to the step S413. If the judgment result of thestep S409 is positive, then the CPU 22 reads, via the input circuit 32and the BAC 23, the output data from the A-D converter 13 which datacorresponds to an analog output of the wind velocity sensor 10 andindicates the actual wind velocity WV (step S410), and determineswhether the wind velocity WV is higher than the lower limit value WVL ornot in order to perform the auxiliary product acceptance/rejectionjudgment based on the wind velocity (step S411). If the judgment resultin the step S411 is positive, then the CPU 22 determines whether thewind velocity WV is below the upper limit value WVH or not (step S412).If the judgment result of the step S411 or S412 is negative, which meansthat the wind velocity deviates from the tolerance limits, there is apossibility of a molding failure having occurred, and therefore, afailure signal is sent out (step S414), then the process of FIG. 3 forthe molding cycle is terminated.

If both judgement results of the steps S411 and S412 are positive, whichmeans that the wind velocity is within the tolerance limits, then it isdetermined that all the open air temperature, die surface temperature,and the wind velocity are within the tolerance limits. In this case, inaddition to the auxiliary product acceptance/rejection judgmentprocesses which are implemented in the aforementioned procedures, thenormal product acceptance/rejection judgement process is carried out(step S413). Then, in accordance with the normal productacceptance/rejection judgement result, the product produced from thatmolding cycle is carried to the non-defectives storing space or thedefectives storing space as described above.

The present invention is not limited to the foregoing embodiment but isavailable in diverse variations. For instance, if the injection moldingmachine is operated in an operating environment where humidity cansignificantly change, an auxiliary product acceptance/rejection judgmentprocess based on the humidity around the injection molding machine whichprocess is similar to those described above may be carried out, using ahumidity sensor 14 and an A-D converter 15 shown with broken lines inFIG. 1.

What is claimed is:
 1. A product acceptance/rejection judgment methodfor an injection molding machine, comprising the steps of:(a) detectingat least one operating parameter value which directly indicates anambient property of an injection molding machine operating environmentinvolved in determining whether a product is acceptable or not; and (b)determining that a molding failure has occurred when the at least oneoperating parameter value detected in step (a) deviates from tolerancelimits thereof.
 2. The product acceptance/rejection judgment methodaccording to claim 1, wherein the operating parameter value indicatesone of a temperature around the injection molding machine, a windvelocity around the injection molding machine, and a humidity around theinjection molding machine.
 3. The product acceptance/rejection judgmentmethod according to claim 1, further comprising the step of (c)selecting at least one of a plurality of operating parameters in advancefor the at least one operating parameter value to be detected in step(a).
 4. The product acceptance/rejection judgment method according toclaim 1,wherein the at least one operating parameter value includesvalues of a plurality of operating parameters detected in step (a), andwherein it is determined in step (b) that the molding failure hasoccurred if one of the values of the operating parameters detected instep (a) deviates from a tolerance limit thereof.
 5. The productacceptance/rejection judgment method according to claim 4,furthercomprising the step of (c) selecting at least two of the operatingparameters in advance, and wherein at least one operating parametervalue detected in step (a) includes values of the at least two operatingparameters selected in advance in step (c).
 6. A productacceptance/rejection judgment method for an injection molding machine,comprising the steps of:(a) selecting for detection at least twooperating parameters from among surface temperature of a die of theinjection molding machine, ambient temperature around the injectionmolding machine, wind velocity around the injection molding machine, andhumidity around the injection molding machine; (b) detecting duringoperation of the injection molding machine values of the at least twooperating parameters selected in step (a); and (c) determining that amolding failure has occurred when the values of any of the at least twooperating parameters detected in step (b) deviate from tolerance limitsthereof.
 7. A product acceptance/rejection judgment method for aninjection molding machine, comprising:(a) detecting values of aplurality of operating parameters, including at least two of a surfacetemperature of a die of the injection molding machine, a temperaturearound the injection molding machine, a wind velocity around theinjection molding machine, and a humidity around the injection moldingmachine; and (b) determining that a molding failure has occurred if anyof the values detected in step (a) deviate from a tolerance limitthereof.